<template>
	<ul class="list">
		<li 
      class="item" 
      v-for="item of letters"
      :key="item"
      :ref="item"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick"
    >{{item}}</li>
	</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
  props: {
    cities: Object
  }, 
  computed: {
    letters() {
      const letters = [];
      for(let i in this.cities) {
        letters.push(i);
      }
      return letters
    }
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated() {
    this.startY = this.$refs['A'][0].offsetTop;
  },
  methods: {
    handleLetterClick(e) {
      this.$emit('change', e.target.innerText);
    },
    handleTouchStart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if(this.touchStatus) {
        if(this.timer) {
          clearTimeout(this.timer);
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79;
          const index = Math.floor((touchY - this.startY) / 20);
          if(index >= 0 && index <= this.letters.length) {
            this.$emit('change', this.letters[index]);
          }
        }, 16)
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      text-align: center
      line-height: .4rem
      color: $bgColor
</style>
